Engineering microorganisms for the production of industrial products has become increasingly attractive in the past decades due to multiple advantages over traditional synthetic methods. Creating new biosynthetic capabilities in microorganisms allows previously limited products, such as therapeutic proteins and complex natural chemicals to be produced and purified at high levels while reducing the use of petroleum-based organic precursors and environmentally destructive chemical processes. In this effort, research has shifted focus from engineering the production of a single recombinant protein to the production of small molecule (e.g., non-protein) products, both natural and synthetic.
Isoprenoids are a highly diverse class of natural products from which numerous commercial flavors, fragrances, chemicals, and medicines are derived. Isoprenoids constitute an extremely large and diverse group of natural products that have a common biosynthetic origin, i.e., a single metabolic precursor, isopentenyl diphosphate (IPP). At least 20,000 isoprenoids have been described. By definition, isoprenoids are made up of so-called isoprene (C5) units. The number of C-atoms present in the isoprenoids is typically divisible by five (C5, C10, C15, C20, C25, C30 and C40), although irregular isoprenoids and polyterpenes have been reported. Isoprenoid compounds are also referred to as “terpenes” or “terpenoids.” Important members of the isoprenoids include the carotenoids, monoterpenoids, sesquiterpenoids, diterpenoids, and hemiterpenes. Carotenoids include, e.g., lycopene, β-carotene, and the like, many of which function as antioxidants. Monoterpenoids include, e.g., menthol and camphor, which are flavor and fragrance agents. Sesquiterpenoids include, e.g., artemisinin, a compound having anti-malarial activity. Diterpenoids include, e.g., taxol, a cancer chemotherapeutic agent.
These valuable compounds are commonly isolated from plants, microbes, and marine organisms where they are naturally produced in small quantities. As such, purification from native sources suffers from low yields, impurities, and excessive consumption of natural resources. Furthermore, most of these compounds are chemically complex, resulting in chemical synthesis routes that are difficult, expensive, and suffer from low yields. For these reasons, the engineering of metabolic pathways to produce large quantities of complex isoprenoids in a tractable biological host presents an attractive alternative to extractions from environmental sources or chemical syntheses. Production consistency, scalability, and efficiency of substrate-to-product conversion of microbial fermentation are of particular importance to producing isoprenoid products on the scale and cost of commodity chemicals.
There is a need in the art for methods of making various products of medical and commercial interest, where the products, or precursors of same, are synthesized in genetically modified host cells.